Recently the demand for fruits and vegetables has increased dramatically with the improvement in feeding levels of the population. To meet such demands, fruits and vegetables are now being shipped from remote places, where the producers are distant from consumers. Accordingly, sometimes the demand and supply for fruits and vegetables become unbalanced. In view of this it is a significant problem to keep fruit and vegetables fresh during temporary storage and during transportation.
Conventionally in order to maintain freshness, it has been the custom to place a freshness retaining agent in the packaged container which holds the fruits or vegetables which retaining agent adsorbs or absorbs the volatile substances produced from the fruits or vegetables so that they are kept from spoiling. This is occasioned by the fact that fruits or vegetables in the packaged container consume oxygen for respiration and generate water vapor, carbonic acid gas, aldehydes, alcohols, esters, ethylene gas, etc. Since the packaged container is closed tightly there is no air flow in it. As time passes less air is present in the packaged container and various volatile gases accumulate which in turn form various other substances in the container. This increases the chance of rot and disease so that the skins, meats, etc. of the fruit or vegetable become limp and discolor thereby decreasing their commercial value. Carbonic acid gas in these tightly closed containers is permitted to be present in amounts of about 2-10%, preferably about 3-7%. However if carbonic acid gas is present in these containers in amounts of 7% or more, aldehydes, alcohols, esters, ethylene as and additional carbonic acid gas are generated which lead to the undesirable effects described above. The generation of ethylene gas and alcohols unfavorably causes the fruit or vegetables to mature much faster, even in amounts of one to several hundreds ppm.
Normally the moisture content of the fruits and vegetables is about 70-95%, preferably about 75-90% in which amount the fruits or vegetables maintain their freshness. However if the moisture content of the fruits and vegetables reaches 95% or more, the moisture is supersaturated and water drops occur with the result that the fruits or vegetables are caused to ripen at a faster rate. On the other hand, in the case where the moisture content is 70% or less, moisture evaporates from the fruits and vegetables with the result that the fruits or vegetables lose weight, shrink and wilt resulting in a loss of freshness.
As can be discerned from the above, there is a close correlation between the freshness of the fruits and vegetables, and the presence of quantities of the various substances described above. The fruits and vegetables in a packaged container are kept fresh by controlling the presence of the quantities of the various substances in the container.
Heretofore, the art has disclosed the use of slaked lime, quick lime, magnesium hydroxide or barium hydroxide for the adsorption and absorption of carbonic acid gas; the use of zeolite, bentonite and active carbon for the adsorption and absorption of ethylene, aldehydes, alcohols, esters, etc., and the use of silica gel, activated clay and alumina gel for the adsorption and absorption of water vapor.
The methods disclosed in the prior art for retaining the freshness of the fruits or vegetables in a packaged container by placing a freshness retaining agent in the container utilizes the freshness retaining agent in a pouch of unwoven cloth. This method is time consuming in that the pouch must first be filled with the retaining agent and placed into the packaged container. A further disadvantage in using the above technique is that the flow of water vapor, carbonic acid gas, ethylene, etc. between the interior of the packaged container and the exterior atmosphere is severely restricted thereby placing an additional burden on the retaining agent which adsorbs and absorbs moisture, carbonic acid gas, ethylene gas, etc. in unnecessary quantities.
A further disadvantage of this technique is that the humidity unusually rises in the packaged container, especially during prolonged storage causing water drops to be formed on the surface of the fruits or vegetables, and the inner walls of packaged container, with the result that the fruits or vegetables degrade. In addition, this leads to favorable conditions for multiplication of the primary parasitic bacteria, which is the major cause for rot.